doc: fix typo in release notes

Bruce Momjian <bruce@momjian.us>

Commit: 7453b8db75a0216fbcc3843e14c2c7266e6a15be
Author: Bruce Momjian <bruce@momjian.us>
Date: 2013-10-09T12:44:52Z
Releases: 9.3.2
doc:  fix typo in release notes

Backpatch through 8.4

Per suggestion by Amit Langote

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